An NHS whistleblower could be sacked for raising concerns that a hospital was fiddling its death rates - bringing into question promises made by ministers to protect those who speak out in the public interest.

Sandra Haynes Kirkbright last year told the Daily Mail that she was "headhunted" by her employer, Royal Wolverhampton NHS Trust, to "fix" its mortality figures.

Mrs Haynes-Kirkbright claimed that "every rule in the book" was broken to try to improve mortality rates, and alleged that she was suspended from her post as a senior "health coder" after refusing to take part in a cover-up.

The trust rejected the allegations of altering the death rates, calling them an "outrageous slur", and said independently-verified evidence "categorically disproved" her claims.

Its chief executive, David Loughton, said at the time: "Improvements in the hospital's mortality rates have been audited and independently verified."

Mrs Haynes-Kirkbright was suspended by the trust after allegations of bullying, harassment, persistent swearing and unprofessional behaviour were made against her by colleagues through their union in April 2012.

Last week she received an email ordering her to attend a disciplinary hearing for leaking information about the trust, the Mail said.

It also warned she could be fired for having spoken out.

In the emailed letter, hospital managers claimed she had "behaved recklessly or negligently in disclosing information regarding the Trust to an external source without the Trust's authorisation to do so", and accused her of breaching employment contracts by speaking to the press.

She was warned "this may result in formal disciplinary action, not excluding dismissal".

The threat raises further questions about protection for whistleblowers following the Mid Staffordshire scandal, in which hundreds of patients are believed to have died because of poor care.

In March last year Health Secretary Jeremy Hunt called for a "culture of openness and transparency" to prevent another case like Mid Staffs.

He said at the time: ''The era of gagging NHS staff from raising their real worries about patient care must come to an end.''

Last night the chairman of the Health Select Committee, Tory MP Stephen Dorrell warned that hospitals trying to sack whisteblowers could face action.

He told the Mail: 'If it can be shown information has been disclosed in the public interest then any attempt to take disciplinary action against that person should prompt action against the hospital by NHS management."

Mrs Haynes-Kirkbright ,a health coder who recorded details of the care received by patients, claimed conditions at Wolverhampton were as bad or worse as those at the Stafford trust.

She believed that the hospital wanted to "fix" its death rates rather than improve patient care, and claimed coders were recording too many deaths at the hospital under "palliative care", the Mail said, which as they were classed as "unavoidable" would not alter the hospital's mortality rate.

Responding to those allegations, Mr Loughton said: "We categorically deny all the allegations and have provided detailed evidence to the Daily Mail to support our position that the suggestion of any wrong-doing is simply not true."